Control device for injection molding machine

ABSTRACT

A control device includes: a memory  29   r  for storing, in a process from a mold tool  10  being open until being closed, the value X(t) of a current flowing in a motor  3  at multiple points in time synchronized to the closing command signal; a mean-and-variance calculating for each of the points in time means for calculating a mean value Mx(t) and a variance value Vx(t) that correspond to current values X(t) that have been read from the memory  29   r ; a threshold calculating means for calculating a current threshold Xf(t) for each of the points in time using the mean value Mx(t) and the variance value Vx(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Xf(t)=Mx(t)+N·{Vx(t)} 1/2    
     where N is a constant and not less than 3; and 
     a foreign object determining unit  29  for comparing the current threshold Xf(t) and the current value X(t) at each of the points in time to determine whether there is an abnormality according to whether the current value X(t) exceeds the current threshold Xf(t) a predetermined number m of times.

TECHNICAL FIELD

A first instance of the conventional art for a control device for aconventional injection molding machine is described in Japanese PatentPublication No. 2515355, and a second instance of the conventional artis described in Japanese Patent Publication No. 3080617. In the firstinstance of the conventional art, when a mold closing operation iscompleted normally, the electrical current at each point in time duringthe normal mold closing operation is designated as a reference value,and the reference value plus an offset value is designated as athreshold. In the next mold closing operation, the previous thresholdand the electrical current in the present mold closing operation arecompared. If the electrical current in the present mold closingoperation is larger, it is determined that a malfunction has arisen inthe mold tool.

In the second instance of the conventional art, a disturbance observeris installed to estimate disturbance torque at each point in time. Athreshold is calculated by adding a shift amount K, for determining atolerance range, to the mean value of disturbance torques during aplurality of repetitions of the mold closing operation in a prior normalperiod. The threshold and the disturbance torque estimated for thepresent mold closing operation are compared. If the present disturbancetorque exceeds the threshold, it is determined that a malfunction ispresent.

However, in the first and the second instances of the conventional art,performance for detection of foreign objects significantly variesdepending on the values designated for the offset or the shift amount.Specifically, if the offset value is designated to be too small,although sensitivity is enhanced, erroneous detection occurs.Conversely, if the offset value is designated to be too large, erroneousdetection can be prevented, but foreign objects cannot be detected withgood sensitivity. Therefore, there has been a problem in that, in orderto find an appropriate offset value, the reference value/mean value mustbe compared, on a display or the like, with the detected currentvalue/estimated disturbance torque value, and the offset/shift amountmust be manually adjusted by trial and error in order that in the normalstate the detected current value or the estimated disturbance torquedoes not exceed the threshold.

Moreover, there has been another problem in that, since the mostappropriate offset value is different depending on the mold or the moldclosing operation command pattern for molding, the offset amount or theshift amount must be adjusted again when the mold or the mold closingoperation command pattern is changed.

Furthermore, there has been another problem in that in the conventionalart the offset/shift amount from the reference value/mean value isdesignated uniformly, yet the most appropriate offset/shift amountvaries at each point in time depending on such factors as the type ofmold.

DISCLOSURE OF THE INVENTION

The invention is made to resolve the above-described problems, and aimsto provide a control device for an injection molding machine, in whichthresholds for determination can be automatically acquired, and it canbe determined at an early stage according to the thresholds whether aforeign object is present within the mold tool—whether normal orabnormal.

In a control device for an injection molding machine, for opening andclosing a mold tool by driving a motor based on an opening and a closingcommand signal, the control device for an injection molding machinerelevant to a first aspect of the invention includes: a currentdetection means for, in a process from the mold tool being open untilbeing closed, detecting at multiple points in time synchronized to theclosing command signal the value X(t) of a current flowing in the motor;a storage means for storing, with the process being repeated A times,respective current values X(t) corresponding to each of the points intime; a mean-and-variance calculating means for calculating for each ofthe points in time a mean value Mx(t) and a variance value Vx(t) thatcorrespond to current values X(t) that have been read from the storagemeans; a threshold calculating means for calculating a current thresholdXf(t) for each of the points in time using the mean value Mx(t) and thevariance value Vx(t) from an arbitrary number of times up to (A−1)times, according to the following equation:Xf(t)=Mx(t)+N·{Vx(t)}^(1/2)

where N is a constant and not less than 3; and

a determining means for comparing the current threshold Xf(t) and thecurrent value X(t) at each of the points in time to determine whetherthere is an abnormality according to whether the current value X(t)exceeds the current threshold Xf(t) a predetermined number m of times.

In a control device for an injection molding machine, for opening andclosing a mold tool by driving a motor based on an opening and a closingcommand signal, the control device for an injection molding machinerelevant to a second aspect of the invention includes: a detection meansfor, in a process from the mold tool being open until being closed,detecting at multiple points in time synchronized to the closing commandsignal the value Y(t) of the velocity or position of the motor; astorage means for storing, with the process being repeated A times,respective velocity or position values Y(t) corresponding to each of thepoints in time; a mean-and-variance calculating means for calculatingfor each of the points in time a mean value My(t) and a variance valueVy(t) that correspond to velocity or position values Y(t) that have beenread from the storage means; a threshold calculating means forcalculating a velocity or position threshold Yf(t) for each of thepoints in time using the mean value My(t) and the variance value Vy(t)from an arbitrary number of times up to (A−1) times, according to thefollowing equation:Yf(t)=My(t)−N·{Vy(t)}^(1/2)

where N is a constant and not less than 3; and

a determining means for comparing the threshold Yf(t) and the velocityor position value Y(t) at each of the points in time to determinewhether there is an abnormality according to whether the velocity orposition value Y(t) is below the threshold Yf(t) a predetermined numberm of times.

In a control device for an injection molding machine, for opening andclosing a mold tool by driving a motor based on an opening and a closingcommand signal, the control device for an injection molding machinerelevant to a third aspect of the invention includes: a currentdetection means for, in a process from the mold tool being open untilbeing closed, detecting at multiple points in time synchronized to theclosing command signal the value X(t) of a current flowing in the motor;a storage means for storing, with the process being repeated A times,respective current values X(t) corresponding to each of the points intime; a mean-and-variance calculating means for calculating for each ofthe points in time a mean value Mx(t) and a variance value Vx(t) ofcurrent values X(t) that have been read from the storage means; anormalization calculating means for converting the current values X(t)for each of the points in time into normalized values Zx(t) using themean value Mx(t) and the variance value Vx(t) from an arbitrary numberof times up to (A−1) times, according to the following equation:Zx(t)={X(t)−Mx(t)}/{Vx(t)}^(1/2); and

a determining means for, after determining whether the normalized valueZx(t) at each of the points in time exceeds a predetermined valueN′(N′>2), if the normalized value exceeds the predetermined value N′,determining whether there is an abnormality according to whether thenormalized value Zx(t) exceeds the normalized value Zx(t−1), at onepoint in time prior to that of the normalized value Zx(t), apredetermined number m′ of times.

In a control device for an injection molding machine, for opening andclosing a mold tool by driving a motor based on an opening and a closingcommand signal, the control device for an injection molding machinerelevant to a fourth aspect of the invention includes: a detection meansfor, in a process from the mold tool being open until being closed,detecting at multiple points in time synchronized to the closing commandsignal the value Y(t) of the velocity or position of the motor; astorage means for storing, with the process being repeated A times,respective velocity or position values Y(t) corresponding to each of thepoints in time; a mean-and-variance calculating means for calculatingfor each of the points in time a mean value My(t) and a variance valueVy(t) of velocity or position values Y(t) that have been read from thestorage means; a normalization calculating means for converting thevelocity values Y(t) for each of the points in time into normalizedvalues Zy(t) using the mean value My(t) and the variance value Vy(t)from an arbitrary number of times up to (A−1) times, according to thefollowing equation:Zy(t)={Y(t)−My(t)}/{Vy(t}^(1/2); and

a determining means for, after determining whether the normalized valueZy(t) at each of the points in time is below a predetermined value−N′(N′>2), if the normalized value is below the predetermined value −N′,determining whether there is an abnormality according to whether thenormalized value Zy(t) is below the normalized value Zy(t−1), at onepoint in time prior to that of the normalized value Zy(t), apredetermined number m′ of times.

In a control device for an injection molding machine, for opening andclosing a mold tool by driving a motor based on an opening and a closingcommand signal, the control device for an injection molding machinerelevant to a fifth aspect of the invention includes: a detection meansfor detecting the rotational position of the motor as a detectedposition; a control means for controlling the motor based on a positiondeviation that is the difference between a commanded position and thedetected position; a storage means for storing, in a process from themold tool being open until being closed, with the process being repeatedA times, respective position deviation values E(t) corresponding to eachof multiple points in time synchronized to the closing command signal; amean-and-variance calculating means for calculating for each of thepoints in time a mean value Me(t) and a variance value Ve(t) thatcorrespond to position deviation values E(t) that have been read fromthe storage means; a threshold calculating means for calculating aposition deviation threshold Ef(t) for each of the points in time usingthe mean value Me(t) and the variance value Ve(t) from an arbitrarynumber of times up to (A−1) times, according to the following equation:Ef(t)=Me(t)+N·{Ve(t)}^(1/2)

where N is a constant and not less than 3; and

a determining means for comparing the position deviation threshold Ef(t)and the position deviation value E(t) at each of the points in time todetermine whether there is an abnormality according to whether theposition deviation value E(t) exceeds the position deviation thresholdEf(t) a predetermined number m of times.

In a control device for an injection molding machine, for opening andclosing a mold tool by driving a motor based on an opening and a closingcommand signal, the control device for an injection molding machinerelevant to a sixth aspect of the invention includes: a detection meansfor detecting the rotational position of the motor as a detectedposition; a control means for controlling the motor based on a positiondeviation that is the difference between a commanded position and thedetected position; a storage means for storing, with the opening/closingprocess being repeated A times, respective position deviation valuesE(t) corresponding to each of points in time; a mean-and-variancecalculating means for calculating for each of the points in time a meanvalue Me(t) and a variance value Ve(t) of position deviation values E(t)that have been read from the storage means; a normalization calculatingmeans for converting the position deviation values E(t) for each of thepoints in time into normalized values Ze(t) using the mean value Me(t)and the variance value Ve(t) from an arbitrary number of times up to(A−1) times, according to the following equation:Ze(t)={E(t)−Me(t)}/{Ve(t)}^(1/2); and

a determining means for, after determining whether the normalized valueZy(t) at each of the points in time exceeds a predetermined valueN′(N′>2), if the normalized value exceeds the predetermined value N′,determining whether there is an abnormality according to whether thenormalized value Ze(t) exceeds the normalized value Ze(t−1), at onepoint in time prior to that of the normalized value Ze(t), apredetermined number m′ of times.

Based on the first or third aspect of the invention, the control devicefor an injection molding machine relevant to a seventh aspect of theinvention includes: a current limiting means for limiting the currentflowing in the motor when the current reaches a predetermined currentlimit value; a detection means for detecting the rotational position ofthe motor as a detected position; a control means for controlling themotor based on a position deviation that is the difference between acommanded position and the detected position; a storage means forstoring, with the process being repeated A times, respective positiondeviation values E(t) corresponding to each of the points in time; amean-and-variance calculating means for calculating for each of thepoints in time a mean value Me(t) and a variance value Ve(t) thatcorrespond to position deviation values E(t) that have been read fromthe storage means; a threshold calculating means for calculating aposition deviation threshold Ef(t) for each of the points in time usingthe mean value Me(t) and the variance value Ve(t) from an arbitrarynumber of times up to (A−1) times, according to the following equation:Ef(t)=Me(t)+N·{Ve(t)}^(1/2)

where N is a constant and not less than 3; and

a determining means for comparing the position deviation threshold Ef(t)and the position deviation value E(t) at each of the points in time todetermine whether there is an abnormality according to whether theposition deviation value E(t) exceeds the position deviation thresholdEf(t) a predetermined number m of times.

Based on the first or third aspect of the invention, the control devicefor an injection molding machine relevant to an eighth aspect of theinvention includes: a current limiting means for limiting the currentflowing in the motor when the current reaches a predetermined currentlimit value; a control means for controlling the motor based on aposition deviation that is the difference between a commanded positionand the detected position; a storage means for storing, with the processbeing repeated A times, respective position deviation values E(t)corresponding to each of the points in time; a mean-and-variancecalculating means for calculating for each of the points in time a meanvalue Me(t) and a variance value Ve(t) of position deviation values E(t)that have been read from the storage means; a normalization calculatingmeans for converting the position deviation values E(t) for each of thepoints in time into normalized values Ze(t) using the mean value Me(t)and the variance value Ve(t) from an arbitrary number of times up to(A−1) times, according to the following equation:Ze(t)={E(t)−Me(t)}/{Ve(t)}^(1/2); and

a determining means for, after determining whether the normalized valueZy(t) at each of the points in time exceeds a predetermined valueN′(N′>2), if the normalized value exceeds the predetermined value N′,determining whether there is an abnormality according to whether thenormalized value Ze(t) exceeds the normalized value Ze(t−1), at onepoint in time prior to that of the normalized value Ze(t), apredetermined number m′ of times.

Based on the first or third aspect of the invention, the control devicefor an injection molding machine relevant to a ninth aspect of. theinvention includes: a current limiting means for limiting, in theprocess from the mold tool being open until being closed, the currentflowing in the motor when the current reaches a predetermined currentlimit value; a detection means for detecting, in the process from themold tool being open until being closed, the value Y(t) of the velocityor position of the motor at multiple points in time synchronized to theclosing command signal; a storage means for storing, with the processbeing repeated A times, respective velocity or position values Y(t)corresponding to each of the points in time; a mean-and-variancecalculating means for calculating for each. of the points in time a meanvalue My(t) and a variance value Vy(t) that correspond to velocity orposition values Y(t) that have been read from the storage means; athreshold calculating means for calculating a threshold Yf(t) for eachof the points in time using the mean value My(t) and the variance valueVy(t) from an arbitrary number of times up to (A−1) times, according tothe following equation:Yf(t)=My(t)−N·{Vy(t)}^(1/2)

where N is a constant and not less than 3; and

a determining means for comparing the threshold Yf(t) and the velocityor position value Y(t) at each of the points in time to determinewhether there is an abnormality according to whether the velocity orposition value Y(t) is below the threshold Yf(t) a predetermined numberm of times.

Based on the first or third aspect of the invention, the control devicefor an injection molding machine relevant to a tenth aspect of theinvention includes: a current limiting means for limiting, in theprocess from the mold tool being open until being closed, the currentflowing in the motor when the current reaches a predetermined currentlimit value; a detection means for detecting, in the process from themold tool being open until being closed, the value Y(t) of the velocityor position of the motor at multiple points in time synchronized to theclosing command signal; a storage means for storing, with the processbeing repeated A times, respective velocity or position values Y(t)corresponding to each of the points in time; a mean-and-variancecalculating means for calculating for each of the points in time a meanvalue My(t) and a variance value Vy(t) of velocity or position valuesY(t) that have been, read from the storage means; a normalizationcalculating means for converting the velocity values Y(t) for each ofthe points in time into normalized values Zy(t) using the mean valueMy(t) and the variance value Vy(t) from an arbitrary number of times upto (A−1) times, according to the following equation:Zy(t)={Y(t)−My(t)}/{Vy(t)}^(1/2); and

a determining means for, after determining whether the normalized valueZy(t) at each of the points in time is below a predetermined value−N′(N′>2), if the normalized value is below the predetermined value −N′,determining whether there is an abnormality according to whether thenormalized value Zy(t) is below the normalized value Zy(t−1), at onepoint in time prior to that of the normalized value Zy(t), apredetermined number m′ of times.

The mean-and-variance calculating means in the control device for aninjection molding machine relevant to an eleventh aspect of theinvention calculates the mean value and the variance value from thecurrent values X(t), the velocity or position values Y(t), or theposition deviation values E(t) during the latest K cycles of the moldclosing operation.

The mean-and-variance calculating means in the control device for aninjection molding machine relevant to a twelfth aspect of the inventioncalculates the mean value and the variance value from any of the currentvalue X(t), the velocity or position value Y(t), and the positiondeviation value E(t) during the most recent mold closing operation, andfrom any pair of the mean value Mx(t) and the variance value Vx(t), themean value My(t) and the variance value Vy(t), and the mean value Me(t)and the variance value Ve(t) during the previous mold closing operation.

A control device for an injection molding machine relevant to athirteenth aspect of the invention includes: a storage means for storinga plurality of combinations of the value N and the number m, or thevalue N′ and the number m′, a detection sensitivity display means fordisplaying, based on the combinations of the value N and the number m,or the value N′ and the number m′, the level of sensitivity in detectingthat a foreign object is present within the mold tool; and an adjustingmeans for adjusting the level based on what is displayed.

A control device for an injection molding machine relevant to afourteenth aspect of the invention includes a display means for visuallydisplaying the current values X(t) and the current thresholds Yf(t), orthe velocity values Y(t) and the velocity or position thresholds Yf(t).

A control device for an injection molding machine relevant to afifteenth aspect of the invention is characterized in that “at multiplepoints in time synchronized to the closing command signal . . . themotor” in the first through tenth aspect of the invention is replaced by“at multiple positions based on closing position command signals . . .the motor”.

A control device for an injection molding machine relevant to asixteenth aspect of the invention is characterized in that, based on thefirst through tenth aspects of the invention, repeating the process Atimes includes a plurality of repetitions B (B<A) of performing theprocess with the mold tool in an empty state in which plastic is notpoured into the mold tool, and at least one repetition of performing theprocess with the mold tool in a state in which plastic is poured intothe mold tool.

According to the first or second aspect of the invention, the meanvalues Mx(t) or My(t), and the variance values Vx(t) or Vy(t) arecalculated based on the current values X(t) or the velocity or positionvalues Y(t); the current thresholds Xf(t) or the velocity thresholds orthe like Yf(t) are automatically calculated based on the mean valuesMx(t) or My(t), and the variance values Vx(t) or Vy(t); and, whether aforeign object is present within the mold tool is determined based onthe current thresholds Xf(t) or the thresholds Yf(t) for the velocity orthe like; whereby there are benefits in that it becomes unnecessary forthe operator to designate by trial and error the offset/shift amount forthe tolerance range from the mean value in order to determine thethresholds, and that whether a foreign object is present in the moldtool can be precisely determined.

According to the third or fourth aspect of the invention, the meanvalues Mx(t) or My(t), and the variance values Vx(t) or Vy(t) arecalculated based on the current values X(t) or the velocity or positionvalues Y(t); normalized values Zx(t) or Zy(t) are automaticallycalculated based on the mean values Mx(t) or My(t), and the variancevalues Vx(t) or Vy(t); and, whether a foreign object is present withinthe mold tool is determined based on the normalized values Zx(t) orZy(t); whereby there are benefits in that it becomes unnecessary for theoperator to designate as physical values by trial and error theoffset/shift amount for the tolerance range from the mean value in orderto determine the reference values, and that a foreign object in the moldtool can be precisely detected.

According to the fifth or sixth aspect of the invention, the mean valuesMe(t) and the variance values Ve(t) are calculated based on the positiondeviation values E(t); the position deviation thresholds Ef(t) or thenormalized values Ze(t) are automatically calculated based on the meanvalues Me(t) and the variance values Ve(t); and, whether a foreignobject is present within the mold tool is determined based on theposition deviation thresholds Ef(t) or the normalized values Ze(t);whereby there are benefits in that it becomes unnecessary for theoperator to designate as physical values by trial and error theoffset/shift amount for the tolerance range from the mean value in orderto determine reference values, and that whether a foreign object ispresent in the mold tool can be precisely determined.

According to the seventh or eighth aspect of the invention, even if thecurrent limiting means is put into operation, the mean values Me(t) andthe variance values Ve(t) are calculated based on the position deviationvalues E(t); the thresholds Ef(t) or the normalized values Ze(t) areautomatically calculated based on the mean values Me(t) and the variancevalues Ve(t); and, whether a foreign object is present within the moldtool is determined based on the thresholds Ef(t) or the normalizedvalues Ze(t); whereby there are benefits in that it becomes unnecessaryfor the operator to designate by trial and error the offset/shift amountfor the tolerance range from the mean value in order to determine thethreshold values, and that whether a foreign object is present in themold tool can be precisely determined.

According to the ninth or tenth aspect of the invention, even if thecurrent limiting means is put into operation, the mean values My(t) andthe variance values Vy(t) are calculated based on the velocity orposition values Y(t); the thresholds Yf(t) or the normalized valuesZy(t) are automatically calculated based on the mean values My(t) andthe variance values Vy(t); and, whether a foreign object is presentwithin the mold tool is determined based on the thresholds Yf(t) or thenormalized values Zy(t); whereby there are benefits in that it becomesunnecessary for the operator to designate by trial and error theoffset/shift amount for the tolerance range from the mean value in orderto determine, the threshold values, and that whether a foreign object inthe mold tool can be precisely determined.

According to the eleventh aspect of the invention, because the mean andvariance values are calculated from the current values X(t) or thevelocity or position values Y(t) during the latest K cycles of the moldclosing operation, even if the current value X(t) and the velocity orposition value Y(t) change due to variation in the ambient temperature,mechanical friction, or the like, the thresholds or the normalizedvalues can be calculated from the current values X(t) or the velocity orposition values Y(t) only during the latest K cycles. Therefore, thereis a benefit in that the control device is less subject to variations inthe ambient temperature, mechanical friction, or the like.

According to the twelfth aspect of the invention, in addition to thebenefit from the ninth aspect of the invention, there is another benefitin that the storage capacity of the storage means can be reduced.

According to the thirteenth aspect of the invention, because the controldevice includes the detection sensitivity display means for displaying,based on combinations of N and m, or N′ and m′, the level of sensitivityin detecting that a foreign object is present within the mold tool, andthe adjusting means for adjusting the level based on what is displayed,there is a benefit in that the operator can easily set the detectionsensitivity.

According to the fourteenth aspect of the invention, because the displaymeans visually displays the current values X(t) and the currentthresholds Xf(t), or the velocity values Y(t) and the velocity orposition thresholds Yf(t), there is a benefit in that the operator canwatch the status of detecting foreign objects during the mold closingoperation.

According to the fifteenth aspect of the invention, because thedetermining means determines an abnormality using the values of thecurrent flowing in the motor, the velocity or position values of themotor, or the like, at multiple positions based on the closing positioncommand signals, the benefits as in the first through tenth aspects ofthe invention can be achieved by using the closing position commandsignals instead of multiple points in time synchronized to the closingcommand signal.

According to the sixteenth aspect of the invention, because repeatingthe process A times includes performing the process in an empty moldstate in which plastic is not poured into the mold tool, there is abenefit in that it can be detected at an early stage that a foreignobject is stuck within the mold tool when plastic is poured into themold tool.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a mold closing mechanism and a controldevice for an injection molding machine according to a first embodimentof the invention.

FIG. 2 is a memory state diagram indicating state of memory that storesdetected current values, mean values, and variance values correspondingto each of sampling times according to the first embodiment.

FIGS. 3 a and 3 b show a diadram (a) having time-current curves and adiagram (b) illustrating time-velocity curves for the injection moldingmachine according to the first embodiment.

FIG. 4 is a flowchart illustrating the operation of the injectionmolding machine according to the first embodiment.

FIG. 5 is a detailed flowchart illustrating the updating of thresholdsduring the mold closing operation with the mold tool in an empty stateillustrated in FIG. 4.

FIG. 6 is a flowchart illustrating the detailed operation of step S107in FIG. 4.

FIG. 7 is a flowchart illustrating the detailed operation of step S111in FIG. 4.

FIG. 8 is a flowchart illustrating a procedure for updating mean valuesand variance values according to a second embodiment.

FIG. 9 is a flowchart illustrating the operation of the injectionmolding machine according to a third embodiment.

FIG. 10 is a flowchart illustrating the detailed operation of step S307in FIG. 9.

FIG. 11 is a flowchart illustrating the detailed operation of step S311in FIG. 9.

FIG. 12 includes a diagram (a) illustrating time-normalized currentvalues and a diagram (b) illustrating time-normalized velocity valuesfor the injection molding machine according to the third embodiment.

FIG. 13 is a memory state diagram indicating state of memory requiredfor updating mean values and variance values in a fourth embodiment.

FIG. 14 is a flowchart illustrating a procedure for updating mean valuesand variance values in the fourth embodiment.

FIGS. 15 a and 15 b illustrate a mold-protection sensitivity settingscreen according to a fifth embodiment.

FIGS. 16 a and 16 b illustrate a time-current (a) and time-velocity (b)according to a sixth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

An embodiment of the invention will be described using FIG. 1 throughFIG. 3.

FIG. 1 is a block diagram of a mold closing operation mechanism and acontrol device for an injection molding machine; FIG. 2 is a memorystate diagram indicating state of memory that stores detected currentvalues, mean values, and variance values corresponding to samplingtimes; and FIG. 3 includes a diagram (a) illustrating time-currentcurves and a diagram (b) illustrating time-velocity curves for theinjection molding machine.

In FIG. 1, the injection molding machine is configured with a motor 3that is controlled so that a d-axis current and a q-axis current flowtherein, and a timing belt 5 that transmits the rotation of the motor 3to a rotational shaft that has a ball screw.

The operation mechanism is provided with a toggle mechanism 7 thattransforms the rotational movement of the motor 3 into linear movement,with one end portion of the toggle mechanism being stationary and theother end portion being fixed on a movable mold 9; and a fixed mold 11facing the movable mold 9. The movable mold 9 and the fixed mold 11constitute a mold tool 10.

The control device includes: an encoder 21 as a detection means fordetecting, at a large number of sampling times (point in time and periodof time) synchronized to the closing command signal for the mold tool10, the velocity or the position Y(t) of the motor 3; a currentdetection circuit 23 as a current detection means for detecting at eachof the sampling times the value of a q-axis current X(t) flowing in themotor 3; an operation panel 25 through which an operator inputs moldclosing commands, mold opening commands and the like; a commandgenerating unit 26 for creating and generating mold opening/closingcommand signals for the mold tool 10 based on commands inputted throughthe operation panel 25; a drive control unit 27 for calculating, fromthe command signals and the position and the velocity detected by theencoder 21, electrical current commands to be given to the motor 3 andthen applying the d-axis current and the q-axis current to the motor 3based on the electrical current commands; a current limiter 28 as acurrent limiting means for limiting the current flowing in the motor 3to a predetermined current when the current exceeds the predeterminedcurrent; a foreign object detection determining unit 29 for determiningwhether a foreign object is present within the mold tool 10 based on thedetected current and the detected velocity that have been detectedduring the closing process for the mold tool 10; a display unit 31 fordisplaying opening/closing information about the mold tool 10; anabnormal instruction unit 33 for generating an instruction signal thatstops the closing operation of the mold tool 10 or opens the mold toolwhen the foreign object detection determining unit 29 determines duringthe closing operation of the mold tool 10 that a foreign object ispresent; and an instruction switching unit 35 for switching theinstruction signal from a normal instruction signal to an abnormalinstruction signal based on a signal ea that the foreign objectdetection determining unit 29 outputs.

The foreign object detection determining unit 29 has memory 29 rconsisting of RAM that stores the detected current values X(t), thedetected velocity values Y(t), and the like.

<Foreign Object Detection Determining Unit 29>

A. Detected Current

-   (1). The injection molding machine produces a lot of identical    molded products, and includes: the memory 29 r as a storage means    for respectively storing, with a single-cycle process of closing the    mold tool 10 being repeated A times, detected current values X(t)    corresponding to each of the sampling times;-   (2). a mean-and-variance calculating means for calculating for each    of the points in time a mean value Mx(t) and a variance value Vx(t)    that correspond to detected current values X(t) that have been read    from the memory 29 r;-   (3). a reference value calculating means for calculating a current    threshold Xf(t) for each of the sampling times using the mean    current value Mx(t) and the current variance value Vx(t) from an    arbitrary number of times up to (A−1) times, according to the    following equation:    Xf(t)=Mx(t)+N·{Vx(t)}^(1/2)

where N≧3; and

-   (4). a determining means for determining whether there is an    abnormality, by comparing the current threshold Xf(t) and the    detected current value X(t) at each of the points in time, when the    number of times the detected current value X(t) is over the current    threshold Xf(t) exceeds a predetermined number m.    B. Detected Velocity-   (1). The memory 29 r for storing, with the above-described process    being repeated A times, respective velocity values Y(t)    corresponding to each of the above-described points in time;-   (2). a mean-and-variance calculating means for calculating for each    of the points in time a mean value My(t) and a variance value Vy(t)    that correspond to velocity values Y(t) that have been read from the    memory 29 r;-   (3). a reference value calculating means for calculating velocity    thresholds Yf(t) for each of the sampling times using the mean    velocity values My(t) and the velocity variance values Vy(t) from an    arbitrary number of times up to (A−1) times, according to the    following equation:    Yf(t)=My(t)−N·{Vy(t)}^(1/2)

where N≧3; and

-   (4). a determining means for determining whether there is an    abnormality, by comparing the velocity threshold Yf(t) and the    velocity value Y(t) at each of the points in time, when the number    of times the velocity value Y(t) is over the velocity threshold    Yf(t) exceeds a predetermined number m are provided.    <Memory>

The storage structure of the memory 29 r will be described using FIG. 2.Each line in FIG. 2( a) requires T sampling data values for each moldclosing operation, and stores the detected current values X(t) for eachof the sampling times; and each row stores the detected current valuesX(t) for K cycles at each sampling time. The detected current valuexi(t) indicates the data for the i-th line during the mold closingoperation. The detected current values for the newer mold closingprocess are stored in the order line p, line (p−1), line (p−2), . . . ,line 1, line 0, line (K−1), . . . , and line (p+1). Each time a moldclosing operation is completed normally, a ring buffering operation bywhich the latest data overwrites the oldest data line is executed. Apointer p in FIG. 2( b) stores the line indicating the latest detectedcurrent values in FIG. 2( a). As in FIG. 2( c), the mean current valuesMx(t) and the current variance values Vx(t) at each sampling time, andthe sums Sx(t) of the current and the sums Ux(t) of squares of thecurrent, which have been calculated according to the followingequations, are stored.

${{Sx}\mspace{11mu}(t)} = {{\sum\limits_{i = 0}^{K - 1}\;{{xi}\mspace{11mu}(t)\mspace{14mu}{Ux}\mspace{11mu}(t)}} = {\sum\limits_{i = 0}^{K - 1}\;\left\{ {x_{i}(t)} \right\}^{2}}}$

The description above has been made for the current, and meanwhile, meanvelocity values My(t), velocity variance values Vy(t), the sums Sy(t) ofthe velocity, and the sums Uy(t) of squares of the velocity are stored.

${{Sy}\mspace{11mu}(t)} = {{\sum\limits_{i = 0}^{K - 1}\;{{yi}\mspace{11mu}(t)\mspace{14mu}{Uy}\mspace{11mu}(t)}} = {\sum\limits_{i = 0}^{K - 1}\;\left\{ {y_{i}(t)} \right\}^{2}}}$

Here, the detected velocity value yi(t) indicates the data for the i-thline during the mold closing operation.

<Current Threshold and Velocity Threshold>

The setting of the current thresholds and the velocity thresholds willbe described using FIG. 3. FIG. 3 includes a diagram (a) illustratingtime-current curves and a diagram (b) illustrating time-velocity curves,which describe the setting of the thresholds. FIG. 3( a) illustrates arelationship among mean current values Mx(t), current thresholds Xf(t),and N·(current variance values)^(1/2)=N·{Vx(t)}^(1/2) where, during thetime T−1 from starting the mold closing operation at the time t=0 tocompletion, the detection timing of the current to be detected isdetermined according to the constant-period sampling time generated bydividing the time T−1 into many segments. Here, T−1 indicates the moldclosing operation completion time.

The shorter the sampling time period is, the better the detectionprecision. However, if the sampling time is too short, the limits of thecomputational capabilities of the foreign object detection determiningunit 29 and the storage capacity of the memory 29 r storing the detectedcurrent become problematic; accordingly, an appropriate sampling periodis around 100 μsec to 10 msec. And, when a foreign object is stuck inthe mold tool 10, the current is increasingly applied to the motor 3; sothe current thresholds are set in a direction increasing from the meanvalues. Whether a malfunction is present is determined using the numberof times when the detected current exceeds the current threshold.

FIG. 3( b) illustrates a relationship among mean velocity values My(t),velocity thresholds Yf(t), and N·(velocity variancevalues)^(1/2)=N·{Vy(t)}^(1/2); and the velocity to be detected issampled according to sampling period during the time T−1 from startingthe mold closing operation at the time t=0 to completion. Moreover, whena foreign object is stuck in the mold tool 10, the foreign object blocksthe movement of the motor 3, and the velocity of the motor 3 is lowerthan the normal value; so the velocity thresholds are set in a directiondecreasing from the mean velocity values. Whether a malfunction ispresent is determined using the number of times when the detectedvelocity underruns the velocity reference value.

<Operation of the Control Device for the Injection Molding Machine>

The operation of the control device for the injection molding machine ofthe embodiment of the invention will be described using FIG. 1 throughFIG. 4. Firstly, in the state where plastic is not poured into the moldtool 10 (hereinafter, referred to as an empty mold), an operator inputsa mold opening/closing instruction signal to the operation panel 25; andthe command generating unit 26 generates opening/closing command signalsand inputs them via the command switching unit 35 to the drive controlunit 27. The drive control unit 27 applies the current to the motor 3based on the opening/closing command signals, and drives the motor 3 byfeedback control based on the detected position value and the detectedvelocity value, of the motor 3, which have been detected by the encoder21, and the detected current value that has been detected by the currentdetection device 23. The rotational movement of the motor 3 istransformed by the toggle mechanism 7 via the timing belt 5 into linearmovement, which opens and closes the empty mold tool several times toupdate the thresholds (step S101). Step S101 is provided here in orderto determine the presence of a foreign object at an early stage afterthe start of the mold closing operation of the mold tool 10 into whichplastic has been poured. The details of the step S101 will be describedusing the flowchart of FIG. 5. The parameter for indicating time is setto t=0 (step S11). The malfunction detection determining unit 29 detectsthe current value detected and the velocity value detected at eachsampling time during the empty molding operation, and stores them in thememory 29 r (step S15). Whether the mold closing operation has beencompleted is checked (step S21); if it has not been completed, t=t+1 isexecuted (step S23), and then step S15 is executed again.

Meanwhile, if the mold closing operation has been completed in step S21,the malfunction detection determining unit 29 updates the mean currentvalues Mx(t), the current variance values Vx(t), the mean velocityvalues My(t), and the velocity variance values Vy(t) (step S27) usingthe detected current values and the detected velocity values in thelatest mold closing operation stored in the memory 29 r; updates thecurrent threshold Xf(t) and the velocity threshold Yf(t) for each of thesampling times (step S29); and checks whether the predetermined numberof repetitions of the mold closing operation in the empty mold statehave been completed (step S31). If the predetermined repetitions of themold closing operation in the empty mold state have been executed, stepS101 is completed. If the predetermined repetitions of the mold closingoperation in the empty mold state have not been executed here, the stepsS11 through S31 are executed.

Next, in order to produce a desired molded object, a molding cycle inwhich plastic is poured into the mold tool 10 is started, and theparameter for indicating time is set to t=0 (step S103). The malfunctiondetection determining unit 29 detects the current value to be detectedand the velocity value to be detected at each sampling time by thecurrent detection circuit 23 and the encoder 21, respectively, in theprocess for the opening and closing operation of the mold tool 10, andstores them in the memory 29 r (step S105). Thus, with the process forthe opening and closing operation of the mold tool 10 being repeated Atimes, the detected current values and the detected velocity valuescorresponding to each of the sampling times have been stored in thememory 29 r. Here, the above “A times” means the sum of the number oftimes of closing the empty mold in the early stage in step S31 in FIG. 5and the number of times of opening and closing the mold tool 10 intowhich plastic has been poured. The malfunction detection determiningunit 29 calculates as described above the current thresholds Xf(t) inthe mold closing operation up to (A−1) times, and determines whetherthere is an abnormality or not by comparing the detected current valueX(t) and the current threshold Xf(t) at each of the sampling times (stepS107).

FIG. 6 is a diagram illustrating in detail step S107 in FIG. 4. Whetherthe detected current value X(t) exceeds the current threshold Xf(t) isdetermined by comparing the detected current value X(t) and the currentthreshold Xf(t) at the same sampling time (step S131). If the detectedcurrent value exceeds the current threshold, a current malfunctioncounter Cx is incremented by 1 (step S133). The foreign object detectiondetermining unit 29 determines whether the current malfunction counterhas reached a predetermined count m (step S137). If it has reached thecount m, the detected current is determined to be abnormal, and anabnormal signal is generated (step S138).

The abnormal signal ea is inputted to the display unit 31, and thedisplay unit 31 indicates using characters or the like that amalfunction has arisen in the mold tool 10. At the same time, theabnormal signal ea is inputted to the instruction switching unit 35, andthe switch is flipped upward to select the instruction from the abnormalinstruction unit 33. The abnormal instruction unit 33 generates a stopcommand for the mold tool 10, and inputs the stop command signal via theinstruction switching unit 35 to the drive control unit 27. The drivecontrol unit 27 stops applying the voltage to the motor 3. Consequently,the operation of the movable mold 9 is stopped immediately on detectinga foreign object having been stuck in the mold tool 10 (step S109).

Meanwhile, if the detected current does not exceed the current thresholdin step S131, the current malfunction counter Cx is reset to 0 (stepS135), and the detected current is determined to be not abnormal (stepS139). In step 137, if the current malfunction counter has not reachedm, the detected current is likewise determined to be not abnormal (stepS139).

Specifically, if the detected current has exceeded the current thresholdat m consecutive sampling times, the detected current is determined tobe abnormal. This can prevent the mold tool 10 from being damaged due toa foreign object being stuck.

In addition, in the above-described embodiment, the movable mold 9 isstopped by the abnormal signal ea, but the movable mold 9 may instead bereversed.

Next, the malfunction detection determining unit 29 calculates asdescribed above the current thresholds Yf(t) in the mold closingoperation up to (A−1) times, and determines whether there is anabnormality or not by comparing the detected velocity value Y(t) and thevelocity threshold Yf(t) at each of the sampling times (step S111).

FIG. 7 is a diagram illustrating in detail step S111 in FIG. 4. Whetherthe detected velocity value is lower than the velocity threshold isdetermined by comparing the detected velocity value Y(t) and thevelocity threshold Yf(t) at the same sampling time (step S141). If thedetected velocity value is lower, the velocity malfunction counter Cy isincremented by 1 (step S143). If a foreign object is stuck in the moldtool 10, the velocity of the motor 3 becomes lower; so when the detectedvelocity value is lower than the velocity threshold, it is determined tobe abnormal.

Whether the velocity malfunction counter Cy has reached thepredetermined count m is determined (step S147). If it has reached thecount m, the detected velocity is determined to be abnormal, and anabnormal signal is generated (step S148). Based on the abnormal signalea, a process for an abnormality as in the above-described step 109 isexecuted (step S113).

Meanwhile, if the velocity threshold is higher than the detectedvelocity value in step S141, the velocity malfunction counter Cy isreset to 0 (step S145), and the detected velocity is determined to benot abnormal (step S149). In step S147, if the velocity malfunctioncounter has not reached m, the detected velocity is likewise determinedto be not abnormal (step S149).

Specifically, if the detected velocity is lower than the velocitythreshold at m consecutive sampling times, the detected velocity isdetermined to be abnormal.

In step S111, if a malfunction is not present, whether the mold closingoperation has been completed is checked (step S115); if the mold closingoperation has not been completed, the sampling time is incremented by 1(step S123); and the steps S105 through S115 are executed again.

Meanwhile, if the mold closing operation has been completed in stepS115, the detected current values and the detected velocity values inthe latest mold closing operation are read from the memory 29 r; and themean current value Mx(t), the current variance value Vx(t), the meanvelocity value My(t), and the velocity variance value Vy(t) for each ofthe sampling times are updated (step S117). Using the mean currentvalue, the current variance value, the mean velocity value, and thevelocity variance value that have been updated as just noted, and apredetermined value N, the current threshold Xf(t) and the velocitythreshold Yf(t) for each of the sampling times are calculated accordingto the following equations (step S119).Xf(t)=Mx(t)+Nx(Vx(t))^(1/2)Yf(t)=My(t)−Nx(Vy(t))^(1/2)

where a value not smaller than 3 is used for N; preferably, 3<N<10. Thisis because it was confirmed by experiment that false operation occurswhen N is smaller than 3.

The foreign object detection determining unit 29 determines whether adesired number of the molding cycles has been reached (step S121). If ithas not been reached, the steps S103 through S119 are executed.Meanwhile, if it has been reached, the processing is terminated.

Furthermore, the current and the velocity that have positive values havebeen described; however, when the current value X(t) and the velocityvalue Y(t) are negative values, the thresholds are designated as in thefollowing equations:Xf(t)=Mx(t)−Nx(Vx(t))^(1/2)Yf(t)=My(t)+Nx(Vy(t))^(1/2)

Moreover, in the above-described steps S131 or S141, if the detectedcurrent value or the detected velocity value has a negative value,whether “X(t)<Xf(t)” or “Y(t)>Yf(t)”, respectively, is to be checked.

As described above, the mean values Mx(t) or My(t), and the variancevalues Vx(t) or Vy(t) are calculated based on the current values X(t) orthe velocity values Y(t); the current thresholds Xf(t) or the velocitythresholds Yf(t) are automatically calculated based on the mean valuesMx(t) or My(t), and the variance values Vx(t) or Vy(t); and, whether aforeign object is present in the mold tool 10 is determined based on thecurrent thresholds Xf(t) or the velocity thresholds Yf(t); whereby itbecomes unnecessary for the operator to designate by trial and error theoffset/shift amount for the tolerance range from the mean value in orderto determine the thresholds, and whether a foreign object is present inthe mold tool can be precisely determined.

When a mold closing operation is executed in particular for acomplicated-structure mold tool such as a mold tool with a slide core,the variance of the current or the velocity at each time t is sometimeslarge and sometimes small. According to the embodiment, at a point intime when the variance of the current or the velocity is large, becausethe variance Vx(t) or Vy(t) is a large value, there is a tendency forthe threshold to become larger. Owing to this tendency, there is abenefit in that the erroneous detection that a foreign object is presenteven in a normal state can be prevented by dulling the sensitivity at alarge-variance point in time. Meanwhile, because at a point in time whenthe variance is small, the variance Vx(t) or Vy(t) is a small value,there is a tendency for the threshold to become smaller. Owing to thistendency, there is a benefit in that a foreign object can be preciselydetected by sharpening the sensitivity at a small-variance point intime.

Furthermore, even if the data variance varies as the mold closingoperation is repeated, Vx(t) or Vy(t) characteristically varies inaccordance with the variation in the data variance, and there is abenefit in that appropriate thresholds can be designated.

Moreover, generally, the drive control unit 27 introduces a feedbackcontrol that compares the instruction signal and the detected presentvalue, and that outputs the current in accordance with that difference;whereby, even if a foreign object is stuck in the mold tool, the drivecontrol unit tries to enlarge the current flow so as to follow theinstruction as long as there is capacity to generate the current. Forthis reason, there is a tendency that, when a foreign object is trapped,a malfunction often manifests itself firstly in the current, and next inthe velocity, the position, or the position deviation. However, when thelimit value for the current limiter 28 in the control device is small,and the current limiter 28 is put into operation, a malfunction is notlikely to manifest itself in the detected current even if a foreignobject is stuck in the mold tool; whereby the precision in determining aforeign object malfunction by the current detection decreases. Givensuch circumstances, even if the current flowing in the motor 3increases, putting the current limiter 28 into operation, the foreignobject determining unit 29 makes a determination based on the abnormalvelocity value Y(t), whereby the foreign object determination can beprecisely performed.

In the above-described embodiment, the foreign object determination isperformed using both the current data and the velocity data; however, incases where the current limit value is large or the memory capacity islimited, only either the current or the velocity may be used todetermine whether a foreign object is present.

Moreover, in step S107 in the above-described embodiment, the foreignobject detection determining unit 29 calculates the current thresholdsXf(t) in the mold closing operation up to (A−1) times; however, this maybe an arbitrary number of times up to (A−1) times, more specifically,(A−2) times or (A−3) times.

Embodiment 2

Even in the detected current values or the detected velocity valuesduring the mold closing process according to identical mold closingcommand signals, global variations, which are minute but graduallyincrease or decrease at all sampling times, sometimes arise in thedetected current values or the detected velocity values due to theambient temperature, mechanical friction, or the like, other than thedetected value variations in repeating the mold closing operation.Accordingly, determination of an abnormality can be performed moreappropriately using the thresholds calculated from the mean and variancevalues of the detected current values and the detected velocity valuesonly in the latest several cycles than using the thresholds calculatedfrom the mean and variance values for each of the sampling times basedon all the detected values from immediately after starting the moldopening/closing cycles up to the most recent cycle.

A mean-and-variance calculating means for the malfunction detectiondetermining unit 29 in another embodiment of the invention in which sucha phenomenon is considered will be described according to the flowchartof FIG. 8.

FIG. 8 corresponds to the calculation and updating, from the detectedcurrent values and the detected velocity values, of the mean currentvalues, the current variance values, the mean velocity values, and thevelocity variance values for each of the sampling times in theabove-described step S117 in FIG. 4 and the above-described step S27 inFIG. 5.

The malfunction detection determining unit 29 removes the effects of thevalues detected K+1 times before from the sum Sx(t) of the current, thesum Ux(t) of squares of the current, the sum Sy(t) of the velocity, andthe sum Uy(t) of squares of the velocity (step S151). The time-seriesdetection values of the most recent normally completed mold closingoperation are written in the line p, which indicates the newest line, inthe memory 29 r (step S153). In order to reflect the effects of thedetected values in the sum Sx(t) of the current, the sum Ux(t) ofsquares of the current, the sum Sy(t) of the velocity, and the sum Uy(t)of squares of the velocity that have been written as above, thecomputation illustrated in FIG. 8 is performed (step S155); and the meancurrent value Mx(t) and the current variance value Vx(t) are calculatedfrom the sum Sx(t) of the current and the sum Ux(t) of squares of thecurrent according to the following equations (step S157).

$\begin{matrix}{{{Mx}\mspace{11mu}(t)} = {{\frac{1}{K}{\sum\limits_{i = 0}^{K - 1}\;{x_{i}\mspace{11mu}(t)}}} = {\frac{1}{K}{Sx}\mspace{11mu}(t)}}} \\{{{Vx}\mspace{11mu}(t)} = {\frac{1}{K}{\sum\limits_{i = 0}^{K - 1}\;\left( {{x_{i}\mspace{11mu}(t)} - {M\;{x(t)}}} \right)^{2}}}} \\{= {{\frac{1}{K}{\sum\limits_{i = 0}^{K - 1}\;\left\{ {x_{i}\mspace{11mu}(t)} \right\}^{2}}} - {\frac{1}{K}\left( {\sum\limits_{i = 0}^{K - 1}{x_{i}\mspace{11mu}(t)}} \right)^{2}}}} \\{= {\frac{1}{K}\left( {{{Ux}\mspace{11mu}(t)} - \left\{ {{Sx}\mspace{11mu}(t)} \right\}^{2}} \right)}}\end{matrix}$

The mean velocity value My(t) and the velocity variance value Vy(t) foreach of the sampling times are calculated in the same way (step S159).The pointer for indicating the latest line is incremented (step S161); acheck is made as to whether the pointer p equals K (step S163); and ifthe pointer equals K, the pointer p is reset to 0 (step S165).

Moreover, when the combination of the present embodiment and theEmbodiment 1 is carried out, the mold closing operation must be repeatedat least K times in the initial stage.

Embodiment 3

There is a tendency that, when a foreign object is stuck in the moldtool 10, both the current flowing in the motor 3 and the velocity of themotor 3 increasingly depart from the mean values as time passes. Thevelocity of the motor 3 gradually decreases because the mold tool 10 isprevented from moving forward by the foreign object that is stuck. Inaddition, when the foreign object is stuck in the mold tool 10, thecurrent flowing in the motor 3 increases so as to follow the instructionof the drive control unit 27 because the closing operation for the moldtool 10 is performed by feedback control.

An embodiment of the invention in which a foreign object is detectedassuredly at an early stage using the above-described phenomenon will bedescribed according to the flowchart of FIG. 9. Symbols in FIG. 9 thatare identical to those in FIG. 4 indicate the corresponding identicalsteps; and their descriptions will be omitted.

In FIG. 9, the steps S107 and S111 in FIG. 4 are replaced with stepsS307 and S311, respectively, and additionally, the step S119 in FIG. 4is eliminated.

FIG. 10 is a flowchart illustrating details of step S307 in FIG. 9. Themalfunction detection determining unit 29 calculates a normalizedcurrent value from the mean value and the variance value at eachsampling time (step S371). More specifically, the normalized currentvalue Zx(t) is calculated from the detected current value X(t), the meancurrent value Mx(t), and the current variance value Vx(t) according tothe following equation.Zx(t)={X(t)−Mx(t)}/{Vx(t)}^(1/2)

The normalized current value Zx(t) is an indicator that indicatesdisplacement from the mean value of the detected current values; thecloser to 0 the normalized current value is, the closer to the meanvalue; and the further from 0 the normalized value is, the larger thedisplacement from the mean value. This will be described using FIG. 12,which illustrates time vs. normalized current value, and time vs.normalized velocity value. According to FIG. 12( a), when a foreignobject starts to get stuck at around the time t0, the normalized currentvalue increases as time passes, and then the normalized current valueexceeds a predetermined value N′.

The malfunction detection determining unit 29 determines whether thecurrent malfunction counter Cx is 0 (step S372) to check if thenormalized current value has exceeded the initial threshold value N′ atthe previous sampling time. If the current malfunction counter Cx is 0,the normalized current value Zx(t) and the predetermined initialthreshold value N′ are compared (step S376). Here, N′>2; morepreferably, 2.5<N′<8. The lower limit of N′ is derived from the factthat N′ is a little smaller than N described in Embodiment 1.

If the normalized current value does not exceed the initial thresholdvalue N′, the malfunction detection determining unit 29 resets thecurrent malfunction counter Cx to 0 (step S378). Meanwhile, if thenormalized current value exceeds the initial threshold value, thecurrent malfunction counter Cx is set to 1 (step S377), and it isdetermined that an abnormality is not present in the detected current(step S381). Meanwhile, if the current malfunction counter Cx is not 0in step S372, the normalized current value Zx(t−1) for the previoussampling time and the normalized current value Zx(t) for the presentsampling time are compared (step S373). The reason why the normalizedcurrent value Zx(t) and the normalized current value Zx(t−1) arecompared here is to detect at an early stage such a phenomenon that, asdescribed above, when a foreign object is stuck in the mold tool 10, thecurrent flowing in the motor 3 increasingly departs from the mean valueas time passes.

The malfunction detection determining unit 29 increments the currentmalfunction counter by 1 if the normalized current value Zx(t) for thepresent time is larger; and then, if the current malfunction counterreaches a predetermined count m′, the malfunction detection determiningunit 29 determines that there is an abnormality because a foreign objectis stuck in the mold tool 10 (step S379). Here, m′>3.

In step S373, if the normalized current value Zx(t−1) for the previoustime is larger than the normalized current value Zx(t) for the presenttime, the current malfunction counter is reset to 0 (step S375).

FIG. 11 is a flowchart illustrating details of step S311 in FIG. 9.Detailed descriptions will be omitted because FIG. 11 is almost the sameas FIG. 10; the differences between FIG. 11 and FIG. 10 are as follows:because the normalized data regarding the velocity becomes lower thanthe mean value when a foreign object is stuck, whether a foreign objectis present is determined in step S473 depending on whether thenormalized velocity value Zy(t) for the present time is lower than thenormalized velocity value Zy(t−1) for the previous time; and in stepS476, it is determined whether the normalized velocity value Zy(t) isbelow a predetermined value “−N′”. Here, the value “−N′” is negative,because the velocity decreases due to a foreign object being stuck inthe mold tool 10.

FIG. 12( b) illustrates a graph of time vs. normalized velocity valuewhen a foreign object starts to get stuck at around time t0.

As in Embodiment 1, both the normalized current value and the normalizedvelocity value are used to determine whether there is an abnormality;however, only either the normalized current value Zx(t) or thenormalized velocity value Zy(t) may be used to determine an abnormality.Moreover, instead of the normalized current value or the normalizedvelocity value, normalized values such as a normalized value regardingthe position or a normalized value regarding the position deviation maybe used to determine an abnormity.

Embodiment 4

In the above-described Embodiment 2, because the detected current valuesand the detected velocity values with respect to the number ofrepetitions of the mold closing operation have been stored in the memory29 r, the storage capacity for the product of the number of repetitionsof the mold closing operation and the number of the sampling times hasbeen required. In this embodiment of the invention, an example in whichthe storage capacity of the memory 29 r is small will be described usingFIG. 13.

FIG. 13 indicates the storage structure of the memory 29 r; the detectedcurrent values X(t) for the last one cycle of sampling times during thenormal closing operation are stored as in FIG. 13( a); the mean currentvalues Mx(t) for the corresponding sampling times are stored as in FIG.13( b); and the current variance values Vx(t) for the correspondingsampling times are stored as in FIG. 13( c).

Next, the calculation and updating of the mean current value Mx(t) andthe current variance value Vx(t) for each of the sampling times in theembodiment will be described with reference to the flowchart of FIG. 14.

The processing in FIG. 14 is executed in order to replace the processingfor Embodiment 2—the updating of the mean value and the variance valuein the step S117 in FIG. 4 and in the step S27 in FIG. 5 for Embodiment1.

The malfunction detection determining unit 29 updates the mean currentvalue Mx(t) and the current variance value Vx(t) for each of thesampling times calculated in the previous cycle according to thefollowing equations (step S501).Mx(t)←αX(t)+(1−α)Mx(t)  (1)Vx(t)←β(X(t)−Mx(t))²+(1−β)Vx(t)  (2)

Here, α and β are fixed numbers; where 0<α, β<1, and, more preferably,0.01<α, β<0.3.

Next, the mean velocity value and the velocity variance value regardingthe velocity are calculated according to a similar procedure (stepS503).

It will be described that the mean current value Mx(t) and the currentvariance value Vx(t) calculated according to the above-describedequations (1) and (2) are a type of mean value and variance value,respectively. Recursive application of the above-described equation (1)leads to the following equation.Mx(t)=αx ⁽⁰⁾(t)+α(1−α)x ⁽¹⁾(t)+α(1−α)² x ⁽²⁾+ . . .   (3)

Here, x^((j))(t) represents the detected current value at sampling timet during the mold closing operation j cycles before.

Moreover, because α+α(1−α)+α(1−α)²+ . . . =1, the value calculatedaccording to the above-described equation (3) can be deemed a weightedarithmetic mean value from a plurality of past data values.

Furthermore, the more recent the detected values, the more the detectedvalues are reflected in the mean value calculated according to theabove-described equation (1). Moreover, recursive application of theabove-described equation (2) likewise leads to the following equation.

$\begin{matrix}{{{Vx}\mspace{11mu}(t)} = {{\beta\mspace{11mu}\left( {{x^{(0)}(t)} - {{Mx}^{(0)}(t)}} \right)^{2}} + {\beta\mspace{11mu}\left( {1 - \beta} \right)\left( {{x^{(1)}(t)} - {{Mx}^{(1)}(t)}} \right)^{2}} + {\beta\mspace{11mu}\left( {1 - \beta} \right)^{2}\left( {{x^{(2)}(t)} - {{Mx}^{(2)}(t)}} \right)^{2}} + \ldots}} & (4)\end{matrix}$

Here, Mx^((j))(t) represents the mean value at sampling time tcalculated j cycles before. As described above, the detected valuesometimes gradually increases or decreases, though only by a smallamount, at all sampling times during every mold closing operation due tovariation in the ambient temperature, mechanical friction, or the like.

However, because such a change is extremely slow relative to the moldclosing cycles, the detected values whose closing cycle numbers areclose to each other for each of the sampling times tend to be very closevalues. Consequently, when j is a small number, the approximationaccording to the following equation is possible.Mx ^((i))(t)≈Mx ^((i+j))(t)  (5)

Accordingly, Vx(t) is expressed as in the following equation.

$\begin{matrix}{{{Vx}\mspace{11mu}(t)} \approx {{\beta\mspace{11mu}\left( {{x^{(0)}(t)} - {{Mx}^{(0)}(t)}} \right)^{2}} + {\beta\mspace{11mu}\left( {1 - \beta} \right)\left( {{x^{(1)}(t)} - {{Mx}^{(0)}(t)}} \right)^{2}} + {\beta\mspace{11mu}\left( {1 - \beta} \right)^{2}\left( {{x^{(2)}(t)} - {{Mx}^{(0)}(t)}} \right)^{2}} + \ldots}} & (6)\end{matrix}$

Here, as j becomes large, the approximation in the above-describedequation (5) does not generally apply; however the coefficientβ(1−β)^(j) in the above-described equation (6) becomes small, wherebythe effect of the difference from the approximation on the whole Vx(t)becomes small.

Likewise as mentioned earlier, by β+β(1−β)+β(1−β)²+ . . . =1, Vx(t) canbe deemed as a weighted sum of squares of the differences between thedetected current values and the mean current values Mx⁽⁰⁾(t) for each ofthe sampling times in the past, namely a type of variance value. As inthe case of the mean value, the larger the difference between the recentdetected values and the mean value, the more the values are reflected inthis variance value as in the mean value.

The mean values calculated according to the above-described equations(1) and (2) are mean/variance values for which the more recent the datathe greater the effect. Accordingly, the mean/variance values quicklyfollow subtle changes or the like of the data due to the ambienttemperature or repetition of the mold closing operation. The thresholdscalculated from such mean/variance values are more appropriate formalfunction determination.

According to such a control device for an injection molding machine, thecalculations according to the above-described equations (1) and (2) canbe carried out by storing only the mean and variance values calculatedduring the previous mold closing operation and the detected values thathave been detected this time as illustrated in FIG. 13, whereby there isa benefit in that the storage capacity of the memory 29 r can bereduced.

Embodiment 5

As described in the above embodiment, the preset value N and the currentmalfunction counter m can be set in advance. However, it is sometimesdesirable to adjust the setting of the preset value N and the currentmalfunction counter m in accordance with local circumstances. This isbecause the most appropriate preset value N and current malfunctioncounter m can be changed depending on the type, or the like, of the moldclosing mechanism for the injection molding machine.

Another embodiment of the invention will be described using FIG. 15. InFIG. 15( a), the operation panel includes a control 122 that moves alonga linear slide bar 121, and a mouse pointer 123 for moving the control122 linearly. A detection sensitivity display means is configured so asto indicate on one end of the slide bar 121 “Sensitivity LOW” for thesensitivity in detecting a foreign object within the mold tool 10 and onthe other end of the slide bar 121 “Sensitivity HIGH” in the same way.The slide bar 121, the control 122, and the mouse pointer 123 configurean adjusting means for adjusting the level of detection sensitivity.Here, the smaller the preset value N and the current malfunction counterm are, the better the sensitivity in detecting a foreign object withinthe mold tool. Conversely, the larger they are, the duller thesensitivity.

For example, when the operator wants to set the sensitivity to be high,(N, m) are set equal to (3, 2); and when the operator wants to set thesensitivity to be low, (N, m) are set equal to (10, 20). Namely, whenthe control 122 is moved around “Sensitivity HIGH”, (N, m) are set tosmall values; and when the control 122 is moved around “SensitivityLOW”, (N, m) are set to large values.

Moreover, not only moving the control 122 linearly as described above,but also rotating a volume control 131 as in FIG. 15( b) may beapplicable to change the sensitivity between “Sensitivity LOW” and“Sensitivity HIGH”.

The operator can visually and intuitively set the preset value N and themalfunction counter m using such a sensitivity setting device.

Embodiment 6

Another embodiment of the invention will be described using FIG. 16. Asillustrated in FIG. 16, the current threshold Xf(t) and the detectedcurrent X(t), and the velocity threshold Yf(t) and the detected velocityY(t), calculated as described above, are simultaneously displayed,respectively, on the display unit 31 illustrated in FIG. 1. According tothis, the operator can easily check, by comparing the detected value andthe threshold, whether the present mold closing operation is beingperformed normally. Moreover, the normalized values regarding thecurrent or the velocity described in the above embodiment may bedisplayed together with the preset value N′ for every sampling time.

Embodiment 7

In the above-described embodiment, the foreign object detectiondetermining unit 29 determines whether a malfunction is present based onthe detected current value and the detected velocity value at eachsampling time during the mold closing operation of the mold tool 10.However, the determination may be made depending on the detectedposition at each sampling time. Here, the detected position can beacquired by detecting data from the encoder 21.

In a case where the position is used, when a foreign object is stuck,the position stops short of the normal state because the foreign objectblocks the mold closing operation. Accordingly, the position thresholdYf(t) is expressed as in the following equation.Yf(t)=My(t)−N·{Vy(t)}^(1/2)

where My(t) is the mean position value, and Vy(t) is the positionvariance value.

The position threshold Yf(t) is set as described above, and by checkingwhether the detected position value is below the position threshold, adetermination is made as to whether a foreign object is present.

Embodiment 8

In a control device for operating the opening/closing of the mold tool10 using the motor 3 based on position commands, in a case where themotor is controlled based on the position deviation—the differencebetween the commanded position and the detected position—the positiondeviation corresponding to each of the sampling times may be applicable.

In a case where the position deviation is used, when a foreign object isstuck, the position deviation increases because the target positioncannot be reached. Accordingly, the position deviation threshold Ef(t)is expressed as in the following equation.Ef(t)=Me(t)+N·{Ve(t)}^(1/2)

where Me(t) is the mean position deviation value, and Ve(t) is theposition deviation variance value.

The position deviation threshold Ef(t) is set as described above, and bychecking whether the detected position deviation value exceeds theposition deviation threshold, a determination is made as to whether aforeign object is present.

Embodiment 9

Although in the above-described embodiments, each of the sampling timessynchronized to the closing command signal for the mold tool 10 has beenused for detection timing of the current values X(t) and the like,closing position command signals using positions based on the closingcommand signal for the mold tool 10 may be used for detection timing.More specifically, in the above-described embodiments, the controldevice includes the encoder 21 for detecting, synchronously with theclosing command signal for the mold tool 10, the velocity or thedetected position Y(t) of the motor 3 at each of the sampling times, andthe current detection circuit 23 for detecting the value X(t) of thecurrent flowing in the motor 3 at each of the sampling times. However,if using the closing position command signals for the mold tool 10instead of the sampling times, another encoder 21 for detecting thevelocity or the detected position Y(t) of the motor 3 at a large numberof positions based on the closing position command signals, and anothercurrent detection circuit 23 for detecting the current values X(t)flowing in the motor 3 corresponding to a large number of positionsbased on the closing position command signals are employed, similaroperations and benefits as in the above-described embodiments can beachieved.

INDUSTRIAL APPLICABILITY

As described above, the control device for the injection molding machinerelevant to the invention is suitable for detecting a foreign objectwithin the mold tool.

1. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: a current detection circuit for, in a process from the mold tool being open until being closed, detecting at multiple points in time synchronized to the closing command signal the value X(t) of a current flowing in the motor; a memory for storing, with said process being repeated A times, respective current values X(t) corresponding to each of the points in time; a mean-and-variance calculating means for calculating for each of the points in time a mean value Mx(t) and a variance value Vx(t) that correspond to current values X(t) that have been read from the memory; a threshold calculating means for calculating a current threshold Xf(t) for each of the points in time using the mean value Mx(t) and the variance value Vx(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Xf(t)=Mx(t)+N·{Vx(t)}^(1/2) where N is a constant and not less than 3; and a determining means for comparing the current threshold Xf(t) and the current value X(t) at each of the points in time to determine whether there is an abnormality according to whether the current value X(t) exceeds the current threshold Xf(t) a predetermined number m of times.
 2. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: an encoder for, in a process from the mold tool being open until being closed, detecting at multiple points in time synchronized to the closing command signal the value Y(t) of the velocity or position of the motor; a memory for storing, with said process being repeated A times, respective velocity or position values Y(t) corresponding to each of the points in time; a mean-and-variance calculating means for calculating for each of the points in time a mean value My(t) and a variance value Vy(t) that correspond to velocity or position values Y(t) that have been read from the memory; a threshold calculating means for calculating a velocity or position threshold Yf(t) for each of the points in time using the mean value My(t) and the variance value Vy(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Yf(t)=My(t)−N·{Vy(t)}^(1/2) where N is a constant and not less than 3; and a determining means for comparing the threshold Yf(t) and the velocity or position value Y(t) at each of the points in time to determine whether there is an abnormality according to whether the velocity or position value Y(t) is below the threshold Yf(t) a predetermined number m of times.
 3. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: a current detection circuit for, in a process from the mold tool being open until being closed, detecting at multiple points in time synchronized to the closing command signal the value X(t) of a current flowing in the motor; a memory for storing, with said process being repeated A times, respective current values X(t) corresponding to each of the points in time; a mean-and-variance calculating means for calculating for each of the points in time a mean value Mx(t) and a variance value Vx(t) of current values X(t) that have been read from the memory; a normalization calculating means for converting the current values X(t) for each of the points in time into normalized values Zx(t) using the mean value Mx(t) and the variance value Vx(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Zx(t)={X(t)−Mx(t)}/{Vx(t)}^(1/2); and a determining means for, after determining whether the normalized value Zx(t) at each of the points in time exceeds a predetermined value N′(N′>2), if the normalized value exceeds the predetermined value N′, determining whether there is an abnormality according to whether the normalized value Zx(t) exceeds the normalized value Zx(t−1), at one point in time prior to that of the normalized value Zx(t), a predetermined number m′ of times.
 4. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: an encoder for, in a process from the mold tool being open until being closed, detecting at multiple points in time synchronized to the closing command signal the value Y(t) of the velocity or position of the motor; a memory for storing, with said process being repeated A times, respective velocity or position values Y(t) corresponding to each of the points in time; a mean-and-variance calculating means for calculating for each of the points in time a mean value My(t) and a variance value Vy(t) of velocity or position values Y(t) that have been read from the memory; a normalization calculating means for converting the velocity or position values Y(t) for each of the points in time into normalized values Zy(t) using the mean value My(t) and the variance value Vy(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Zy(t)={Y(t)−My(t)}/{Vy(t)}^(1/2); and a determining means for, after determining whether the normalized value Zy(t) at each of the points in time is below a predetermined value −N′(N′>2), if the normalized value is below the predetermined value −N′, determining whether there is an abnormality according to whether the normalized value Zy(t) is below the normalized value Zy(t−1), at one point in time prior to that of the normalized value Zy(t), a predetermined number m′ of times.
 5. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: an encoder for detecting the rotational position of the motor as a detected position; a control means for controlling the motor based on a position deviation that is the difference between a commanded position and the detected position; a memory for storing, in a process from the mold tool being open until being closed, with said process being repeated A times, respective position deviation values E(t) corresponding to each of multiple points in time synchronized to the closing command signal; a mean-and-variance calculating means for calculating for each of the points in time a mean value Me(t) and a variance value Ve(t) that correspond to position deviation values E(t) that have been read from the memory; a threshold calculating means for calculating a position deviation threshold Ef(t) for each of the points in time using the mean value Me(t) and the variance value Ve(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Ef(t)=Me(t)+N·{Ve(t)}^(1/2) where N is a constant and not less than 3; and a determining means for comparing the position deviation threshold Ef(t) and the position deviation value E(t) at each of the points in time to determine whether there is an abnormality according to whether the position deviation value E(t) exceeds the position deviation threshold Ef(t) a predetermined number m of times.
 6. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: an encoder for detecting the rotational position of the motor as a detected position; a control means for controlling the motor based on a position deviation that is the difference between a commanded position and the detected position; a memory for storing, in a process from the mold tool being open until being closed, with said process being repeated A times, respective position deviation values E(t) corresponding to each of multiple points in time synchronized to the closing command signal; a mean-and-variance calculating means for calculating for each of the points in time a mean value Me(t) and a variance value Ve(t) of position deviation values E(t) that have been read from the memory; a normalization calculating means for converting the position deviation values E(t) for each of the points in time into normalized values Ze(t) using the mean value Me(t) and the variance value Ve(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Ze(t)={E(t)−Me(t)}/{Ve(t)}^(1/2); and a determining means for, after determining whether the normalized value Ze(t) at each of the points in time exceeds a predetermined value N′(N′>2), if the normalized value exceeds the predetermined value N′, determining whether there is an abnormality according to whether the normalized value Ze(t) exceeds the normalized value Ze(t (1), at one point in time prior to that of the normalized value Ze(t), a predetermined number m′ of times.
 7. A control device for an injection molding machine according to claim 1, the control device further comprising: an encoder for detecting the rotational position of the motor as a detected position; a current limiter for limiting the current flowing in the motor when the current reaches a predetermined current limit value; and a control means for controlling the motor based on a position deviation that is the difference between a commanded position and the detected position; wherein, with said process being repeated A times, the memory stores respective position deviation values E(t) corresponding to each of the points in time; wherein the mean-and-variance calculating means calculates for each of the points in time a mean value Me(t) and a variance value Ve(t) that correspond to position deviation values E(t) that have been read from the memory; wherein the threshold calculating means calculates a position deviation threshold Ef(t) for each of the points in time using the mean value Me(t) and the variance value Ve(t) from an arbitrary number of times up to (A (1) times, according to the following equation: Ef(t)=Me(t)+N({Ve(t)}½; and wherein the determining means compares the position deviation threshold Ef(t) and the position deviation value E(t) at each of the points in time to determine whether there is an abnormality according to whether the position deviation value E(t) exceeds the position deviation threshold Ef(t) the predetermined number m of times.
 8. A control device for an injection molding machine according to claim 3, the control device further comprising: an encoder for detecting the rotational position of the motor as a detected position; a current limiter for limiting the current flowing in the motor when the current reaches a predetermined current limit value; a control means for controlling the motor based on a position deviation that is the difference between a commanded position and the detected position; and a threshold calculating means; wherein, with said process being repeated A times, the memory stores respective position deviation values E(t) corresponding to each of the points in time; wherein the mean-and-variance calculating means calculates for each of the points in time a mean value Me(t) and a variance value Ve(t) that correspond to position deviation values E(t) that have been read from the memory; wherein the threshold calculating means calculates a position deviation threshold Ef(t) for each of the points in time using the mean value Me(t) and the variance value Ve(t) from an arbitrary number of times up to (A (1) times, according to the following equation: Ef(t)=Me(t)+N({Ve(t)}½ where N is a constant and not less than 3; and wherein the determining means compares the position deviation threshold Ef(t) and the position deviation value E(t) at each of the points in time to determine whether there is an abnormality according to whether the position deviation value E(t) exceeds the position deviation threshold Ef(t) a predetermined number m of times.
 9. A control device for an injection molding machine according to claim 1, the control device further comprising: an encoder for detecting the rotational position of the motor as a detected position; a current limiter for limiting the current flowing in the motor when the current reaches a predetermined current limit value; a control means for controlling the motor based on a position deviation that is the difference between a commanded position and the detected position; and a normalization calculating means; wherein, with said process being repeated A times, the memory stores respective position deviation values E(t) corresponding to each of the points in time; wherein the mean-and-variance calculating means calculates for each of the points in time a mean value Me(t) and a variance value Ve(t) of position deviation values E(t) that have been read from the memory; wherein the normalization calculating means converts the position deviation values E(t) for each of the points in time into normalized values Ze(t) using the mean value Me(t) and the variance value Ve(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Ze(t)={E(t)(Me(t)}/{Ve(t)}½; and wherein the determining means, after determining whether the normalized value Ze(t) at each of the points in time exceeds a predetermined value N′(N′>2), if the normalized value exceeds the predetermined value N′, determines whether there is an abnormality according to whether the normalized value Ze(t) exceeds the normalized value Ze(t (1), at one point in time prior to that of the normalized value Ze(t), a predetermined number m′ of times.
 10. A control device for an injection molding machine according to claim 3, the control device further comprising: an encoder for detecting the rotational position of the motor as a detected position; a current limiter for limiting the current flowing in the motor when the current reaches a predetermined current limit value; and a control means for controlling the motor based on a position deviation that is the difference between a commanded position and the detected position; wherein, with said process being repeated A times, the memory stores respective position deviation values E(t) corresponding to each of the points in time; wherein the mean-and-variance calculating means calculates for each of the points in time a mean value Me(t) and a variance value Ve(t) of position deviation values E(t) that have been read from the memory; wherein the normalization calculating means converts the position deviation values E(t) for each of the points in time into normalized values Ze(t) using the mean value Me(t) and the variance value Ve(t) from an arbitrary number of times up to (A (1) times, according to the following equation: Ze(t)={E(t)(Me(t)}/{Ve(t)}½; and wherein the determining means, after determining whether the normalized value Ze(t) at each of the points in time exceeds the predetermined value N′(N′>2), if the normalized value exceeds the predetermined value N′, determines whether there is an abnormality according to whether the normalized value Ze(t) exceeds the normalized value Ze(t (1), at one point in time prior to that of the normalized value Ze(t), the predetermined number m′ of times.
 11. A control device for an injection molding machine according to claim 1, the control device further comprising: a current limiter for limiting, in the process from the mold tool being open until being closed, the current flowing in the motor when the current reaches a predetermined current limit value; and an encoder for, in the process from the mold tool being open until being closed, detecting at multiple points in time synchronized to the closing command signal the value Y(t) of the velocity or position of the motor; wherein, with said process being repeated A times, the memory stores respective velocity or position values Y(t) corresponding to each of the points in time; wherein the mean-and-variance calculating means calculates for each of the points in time a mean value My(t) and a variance value Vy(t) that correspond to velocity or position values Y(t) that have been read from the memory; wherein the threshold calculating means calculates a threshold Yf(t) for each of the points in time using the mean value My(t) and the variance value Vy(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Yf(t)=My(t)−N·{Vy(t)}^(1/2); and wherein the determining means compares the threshold Yf(t) and the velocity or position value Y(t) at each of the points in time to determine whether there is an abnormality according to whether the velocity or position value Y(t) is below the threshold Yf(t) the predetermined number m of times.
 12. A control device for an injection molding machine according to claim 3, the control device further comprising: a current limiter for limiting, in the process from the mold tool being open until being closed, the current flowing in the motor when the current reaches a predetermined current limit value; an encoder for, in the process from the mold tool being open until being closed, detecting at multiple points in time synchronized to the closing command signal the value Y(t) of the velocity or position of the motor; and a threshold calculating means; wherein, with said process being repeated A times, the memory stores respective velocity or position values Y(t) corresponding to each of the points in time; wherein the mean-and-variance calculating means calculates for each of the points in time a mean value My(t) and a variance value Vy(t) that correspond to velocity or position values Y(t) that have been read from the memory; wherein the threshold calculating means calculates a threshold Yf(t) for each of the points in time using the mean value My(t) and the variance value Vy(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Yf(t)=My(t)−N·{Vy(t)}^(1/2) where N is a constant and not less than 3; and wherein the determining means compares the threshold Yf(t) and the velocity or position value Y(t) at each of the points in time to determine whether there is an abnormality according to whether the velocity or position value Y(t) is below the threshold Yf(t) a predetermined number m of times.
 13. A control device for an injection molding machine according to claim 1, the control device further comprising: a current limiter for limiting, in the process from the mold tool being open until being closed, the current flowing in the motor when the current reaches a predetermined current limit value; an encoder for,in the process from the mold tool being open until being closed, detecting at multiple points in time synchronized to the closing command signal the value Y(t) of the velocity or position of the motor; and a normalization calculating means; wherein, with said process being repeated A times, the memory stores respective velocity or position values Y(t) corresponding to each of the points in time; wherein the mean-and-variance calculating means calculates for each of the points in time a mean value My(t) and a variance value Vy(t) of velocity or position values Y(t) that have been read from the memory; wherein the normalization calculating means converts the velocity or position values Y(t) for each of the points in time into normalized values Zy(t) using the mean value My(t) and the variance value Vy(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Zy(t)={Y(t)−My(t)}/{Vy(t)}^(1/2); and wherein, after determining whether the normalized value Zy(t) at each of the points in time is below a predetermined value −N′(N′>2), if the normalized value is below the predetermined value −N′, the determining means determines whether there is an abnormality according to whether the normalized value Zy(t) is below the normalized value Zy(t−1), at one point in time prior to that of the normalized value Zy(t), a predetermined number m′ of times.
 14. A control device for an injection molding machine according to claim 3, the control device further comprising: a current limiter for limiting, in the process from the mold tool being open until being closed, the current flowing in the motor when the current reaches a predetermined current limit value; and an encoder for, in the process from the mold tool being open until being closed, detecting at multiple points in time synchronized to the closing command signal the value Y(t) of the velocity or position of the motor; wherein, with said process being repeated A times, the memory stores respective velocity or position values Y(t) corresponding to each of the points in time; wherein the mean-and-variance calculating means calculates for each of the points in time a mean value My(t) and a variance value Vy(t) of velocity or position values Y(t) that have been read from the memory; wherein the normalization calculating means converts the velocity or position values Y(t) for each of the points in time into normalized values Zy(t) using the mean value My(t) and the variance value Vy(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Zy(t)={Y(t)−My(t)}/{Vy(t)}^(1/2); and wherein, after determining whether the normalized value Zy(t) at each of the points in time is below the predetermined value −N′(N′>2), if the normalized value is below the predetermined value −N′, the determining means determines whether there is an abnormality according to whether the normalized value Zy(t) is below the normalized value Zy(t−1), at one point in time prior to that of the normalized value Zy(t), the predetermined number m′ of times.
 15. A control device for an injection molding machine according to claim 1, wherein the mean-and-variance calculating means calculates the mean value Mx(t) and the variance value Vx(t) from the current values X(t) during the latest K cycles of the mold closing operation.
 16. A control device for an injection molding machine according to claim 2, wherein the mean-and-variance calculating means calculates the mean value My(t) and the variance value Vy(t) from the velocity or position values Y(t) during the latest K cycles of the mold closing operation.
 17. A control device for an injection molding machine according to claim 3, wherein the mean-and-variance calculating means calculates the mean value Mx(t) and the variance value Vx(t) from the current values X(t) during the latest K cycles of the mold closing operation.
 18. A control device for an injection molding machine according to claim 4, wherein the mean-and-variance calculating means calculates the mean value My(t) and the variance value Vy(t) from the velocity or position values Y(t) during the latest K cycles of the mold closing operation.
 19. A control device for an injection molding machine according to claim 1, wherein the mean-and-variance calculating means calculates the mean value Mx(t) and the variance value Vx(t) from the current value X(t) during the most recent mold closing operation, and from the mean value Mx(t) and the variance value Vx(t) during the previous mold closing operation.
 20. A control device for an injection molding machine according to claim 2, wherein the mean-and-variance calculating means calculates the mean value My(t) and the variance value Vy(t) from the velocity or position value Y(t) during the most recent mold closing operation, and from the mean value My(t) and the variance value Vy(t) during the previous mold closing operation.
 21. A control device for an injection molding machine according to claim 3, wherein the mean-and-variance calculating means calculates the mean value Mx(t) and the variance value Vx(t) from the current value X(t) during the most recent mold closing operation, and from the mean value Mx(t) and the variance value Vx(t) during the previous mold closing operation.
 22. A control device for an injection molding machine according to claim 4, wherein the mean-and-variance calculating means calculates the mean value My(t) and the variance value Vy(t) from the velocity or position value Y(t) during the most recent mold closing operation, and from the mean value My(t) and the variance value Vy(t) during the previous mold closing operation.
 23. A control device for an injection molding machine according to claim 5, wherein the mean-and-variance calculating means calculates the mean value Me(t) and the variance value Ve(t) from the position deviation value E(t) during the most recent mold closing operation, and from the mean value Me(t) and the variance value Ve(t) during the previous mold closing operation.
 24. A control device for an injection molding machine according to claim 6, wherein the mean-and-variance calculating means calculates the mean value Me(t) and the variance value Ve(t) from the position deviation value E(t) during the most recent mold closing operation, and from the mean value Me(t) and the variance value Ve(t) during the previous mold closing operation.
 25. A control device for an injection molding machine according to claim 7, wherein the mean-and-variance calculating means calculates the mean value Me(t) and the variance value Ve(t) from the position deviation value E(t) during the most recent mold closing operation, and from the mean value Me(t) and the variance value Ve(t) during the previous mold closing operation.
 26. A control device for an injection molding machine according to claim 8, wherein the mean-and-variance calculating means calculates the mean value Me(t) and the variance value Ve(t) from the position deviation value E(t) during the most recent mold closing operation, and from the mean value Me(t) and the variance value Ve(t) during the previous mold closing operation.
 27. A control device for an injection molding machine according to claim 9, wherein the mean-and-variance calculating means calculates the mean value Me(t) and the variance value Ve(t) from the position deviation value E(t) during the most recent mold closing operation, and from the mean value Me(t) and the variance value Ve(t) during the previous mold closing operation.
 28. A control device for an injection molding machine according to claim 10, wherein the mean-and-variance calculating means calculates the mean value Me(t) and the variance value Ve(t) from the position deviation value E(t) during the most recent mold closing operation, and from the mean value Me(t) and the variance value Ve(t) during the previous mold closing operation.
 29. A control device for an injection molding machine according to claim 11, wherein the mean-and-variance calculating means calculates the mean value My(t) and the variance value Vy(t) from the velocity or position value Y(t) during the most recent mold closing operation, and from the mean value My(t) and the variance value Vy(t) during the previous mold closing operation.
 30. A control device for an injection molding machine according to claim 12, wherein the mean-and-variance calculating means calculates the mean value My(t) and the variance value Vy(t) from the velocity or position value Y(t) during the most recent mold closing operation, and from the mean value My(t) and the variance value Vy(t) during the previous mold closing operation.
 31. A control device for an injection molding machine according to claim 13, wherein the mean-and-variance calculating means calculates the mean value My(t) and the variance value Vy(t) from the velocity or position value Y(t) during the most recent mold closing operation, and from the mean value My(t) and the variance value Vy(t) during the previous mold closing operation.
 32. A control device for an injection molding machine according to claim 14, wherein the mean-and-variance calculating means calculates the mean value My(t) and the variance value Vy(t) from the velocity or position value Y(t) during the most recent mold closing operation, and from the mean value My(t) and the variance value Vy(t) during the previous mold closing operation.
 33. A control device for an injection molding machine according to claim 1, wherein the memory stores a plurality of combinations of said value N and said number m; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N and said number m, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 34. A control device for an injection molding machine according to claim 2, wherein the memory stores a plurality of combinations of said value N and said number m; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N and said number m, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 35. A control device for an injection molding machine according to claim 3, wherein the memory stores a plurality of combinations of said value N′ and said number m′; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N′ and said number m′, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 36. A control device for an injection molding machine according to claim 4, wherein the memory stores a plurality of combinations of said value N′ and said number m′; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N′ and said number m′, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 37. A control device for an injection molding machine according to claim 5, wherein the memory stores a plurality of combinations of said value N and said number m; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N and said number m, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 38. A control device for an injection molding machine according to claim 6, wherein the memory stores a plurality of combinations of said value N′ and said number m′; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N′ and said number m′, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 39. A control device for an injection molding machine according to claim 7, wherein the memory stores a plurality of combinations of said value N and said number m; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N and said number m, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 40. A control device for an injection molding machine according to claim 8, wherein the memory stores a plurality of combinations of said value N and said number m; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N and said number m, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 41. A control device for an injection molding machine according to claim 9, wherein the memory stores a plurality of combinations of said value N′ and said number m′; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N′ and said number m′, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 42. A control device for an injection molding machine according to claim 10, wherein the memory stores a plurality of combinations of said value N′ and said number m′; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N′ and said number m′, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 43. A control device for an injection molding machine according to claim 11, wherein the memory stores a plurality of combinations of said value N and said number m; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N and said number m, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 44. A control device for an injection molding machine according to claim 12, wherein the memory stores a plurality of combinations of said value N and said number m; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N and said number m, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 45. A control device for an injection molding machine according to claim 13, wherein the memory stores a plurality of combinations of said value N′ and said number m′; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N′ and said number m′, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 46. A control device for an injection molding machine according to claim 14, wherein the memory stores a plurality of combinations of said value N′ and said number m′; and the control device further comprises: a detection sensitivity display means for displaying, based on the combinations of said value N′ and said number m′, the level of sensitivity in detecting that a foreign object is present within the mold tool; and an adjusting means for adjusting said level based on what is displayed.
 47. A control device for an injection molding machine according to claim 1, the control device further comprising a display means for visually displaying the current values X(t) and the current thresholds Xf(t).
 48. A control device for an injection molding machine according to claim 2, the control device further comprising a display means for visually displaying the velocity or position values Y(t) and the velocity or position thresholds Yf(t).
 49. A control device for an injection molding machine according to claim 5, the control device further comprising a display means for visually displaying the position deviation values E(t) and the position deviation thresholds Ef(t).
 50. A control device for an injection molding machine according to claim 7, further comprising a display means for visually displaying the position deviation values E(t) and the position deviation thresholds Ef(t).
 51. A control device for an injection molding machine according to claim 8, further comprising a display means for visually displaying the position deviation values E(t) and the position deviation thresholds Ef(t).
 52. A control device for an injection molding machine according to claim 11, the control device further comprising a display means for visually displaying the velocity or position values Y(t) and the velocity or position thresholds Yf(t).
 53. A control device for an injection molding machine according to claim 12, the control device further comprising a display means for visually displaying the velocity or position values Y(t) and the velocity or position thresholds Yf(t).
 54. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: a current detection circuit for, in a process from the mold tool being open until being closed, detecting at multiple positions based on closing position command signals the value X(t) of a current flowing in the motor; a memory for storing, with said process being repeated A times, respective current values X(t) corresponding to each of the detected positions; a mean-and-variance calculating means for calculating for each of the detected positions a mean value Mx(t) and a variance value Vx(t) that correspond to current values X(t) that have been read from the memory; a threshold calculating means for calculating a current threshold Xf(t) for each of the detected positions using the mean value Mx(t) and the variance value Vx(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Xf(t)=Mx(t)+N·{Vx(t)}^(1/2) where N is a constant and not less than 3; and a determining means for comparing the current threshold Xf(t) and the current value X(t) at each of the detected positions to determine whether there is an abnormality according to whether the current value X(t) exceeds the current threshold Xf(t) a predetermined number m of times.
 55. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: an encoder for, in a process from the mold tool being open until being closed, detecting at multiple positions based on closing position command signals the value Y(t) of the velocity or position of the motor; a memory for storing, with said process being repeated A times, respective velocity or position values Y(t) corresponding to each of the detected positions; a mean-and-variance calculating means for calculating for each of the detected positions a mean value My(t) and a variance value Vy(t) that correspond to velocity or position values Y(t) that have been read from the memory; a threshold calculating means for calculating a velocity or position threshold Yf(t) for each of the detected positions using the mean value My(t) and the variance value Vy(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Yf(t)=My(t)−N·{Vy(t)}^(1/2) where N is a constant and not less than 3; and a determining means for comparing the threshold Yf(t) and the velocity or position value Y(t) at each of the detected positions to determine whether there is an abnormality according to whether the velocity or position value Y(t) is below the threshold Yf(t) a predetermined number m of times.
 56. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: a current detection circuit for, in a process from the mold tool being open until being closed, detecting at multiple positions based on closing position command signals the value X(t) of a current flowing in the motor; a memory for storing, with said process being repeated A times, respective current values X(t) corresponding to each of the detected positions; a mean-and-variance calculating means for calculating for each of the detected positions a mean value Mx(t) and a variance value Vx(t) of current values X(t) that have been read from the memory; a normalization calculating means for converting the current values X(t) for each of the detected positions into normalized values Zx(t) using the mean value Mx(t) and the variance value Vx(t) from an arbitrary number of times up to (A−1) times, according to the following equation: Zx(t)={X(t)−Mx(t)}/{Vx(t)}^(1/2); and a determining means for, after determining whether the normalized value Zx(t) at each of the detected positions exceeds a predetermined value N′(N′>2), if the normalized value exceeds the predetermined value N′, determining whether there is an abnormality according to whether the normalized value Zx(t) exceeds the normalized value Zx(t (1), at one point in time prior to that of the normalized value Zx(t), a predetermined number m′ of times.
 57. A control device for an injection molding machine, for opening and closing a mold tool by driving a motor based on an opening and a closing command signal, the control device comprising: an encoder for, in a process from the mold tool being open until being closed, detecting at multiple positions based on closing position command signals the value Y(t) of the velocity or position of the motor; a memory for storing, with said process being repeated A times, respective velocity or position values Y(t) corresponding to each of the detected positions; a mean-and-variance calculating means for calculating for each of the detected positions a mean value My(t) and a variance value Vy(t) of velocity or position values Y(t) that have been read from the memory; a normalization calculating means for converting the velocity or position values Y(t) for each of the detected positions into normalized values Zy(t) using the mean value My(t) and the variance value Vy(t) from an arbitrary number of times up to (A (1) times, according to the following equation: Zy(t)={Y(t)(My(t)}/{Vy(t)}½; and a determining means for, after determining whether the normalized value Zy(t) at each of the detected positions is below a predetermined value (N′(N′>2), if the normalized value is below the predetermined value (N′, determining whether there is an abnormality according to whether the normalized value Zy(t) is below the normalized value Zy(t (1), at one point in time prior to that of the normalized value Zy(t), a predetermined number m′ of times. 